I'm wondering if someone could please clear something up for me as I'm getting conflicting advice.

We have a un-braked box trailer that has an empty weight approx 400kgs (exact figures are on the plate... not sure what it is). I was told by the manufacturer that the empty weight doesn't count towards the maximum tow weight and only the load does.

One the other hand, I've been told that both the empty trailer weight plus the load must be below the maximum towing weight.

Which rules applies to the maximum tow weight as specified by the car manufacturer?

Yes MDC, I can see how you'd be confused! The manufacturer of the trailer should know better.

Check the vehicle manufacturer's figures regarding towing. See that they refer to I think it is a phrase like 'aggregate vehicle mass' or some such clarifying statement (;-) meaning the total of the trailer and its load. It is the trailer and its load which is being towed, not just the load without the trailer (conjours up interesting images!).

See what the 'ball weight' limit is as recommended by the vehicle manufacturer. Not how well-endowed the trailer is, but the downward force on the tow ball. For most ordinary 2 wheel-drive vehicles it's around 40 to 50 kilos. You can do a rough check with the unladen trailer by putting the jockey wheel on a bathroom scale. Then with it loaded, do it again and get another figure. Both are just ideas to save you a trip to a public weighbridge.

Take away at least 10 percent from the figures the vehicle manufacturer gives. Experience tells me that if you load your vehicle right up to what they say you can, you could get out and run faster.

Unless you tow with a hugely powerful vehicle and have plenty of money for extra fuel, err on the side of caution with buying a trailer and loading it up. Extra wind resistance and extra weight really chew into the fuel.

It's great to get this sorted out. A trailer weighing 400kgs and a car that can tow 720kgs un-braked doesn't leave me much for packing. It looks like I better start looking at some brakes.

When I had the tow bar fitted they said that regarding tow ball weight, if you can't easily lift the trailer from the hitch then you're probably going to be over the max weight. I'll definitely try the bathroom scale trick though.

We had it fully loaded for the christmas trip and didn't notice any difference in fuel economy. The car isn't overly powerful (Forester XT) but it handled the trailer like it wasn't there.

Hmm I'll definitely have to weigh it then. I would have thought that the manufacturer would get it right, but they didn't even tell me the right thing about towing weights. Now I'm really doubting a few things about this mob.... they came highly recommended by a lot of people and are known to be one of the better ones out there.